LP UVA Introduction. 2 Working Principle. TEL r.a. FAX

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1 CENTRO DI TARATURA SIT N 124 TEL r.a. FAX LP UVA 02 1 Introduction The LP UVA 02 radiometer measures the global irradiance in the UVA spectral region on a plane surface (Watt/m 2 ). The global irradiance is the sum of the direct solar irradiance and of the diffuse irradiance. In order to measure the only UVA radiation diffuse part it s possible to mount the radiometer on the relevant shield ring LP PYRA 12. The radiometer can be used also for monitoring the UVA rays indoors. 2 Working Principle The LP UVA 02 radiometer is based on a solid state sensor which spectral response was suited according to the desired one by means of the use of suitable filters. The relevant response spectral curve is indicated in the figure E+00 Relative spectral response 1.00E E E Lambda (nm) Fig1-1 -

2 The LP UVA 02 is provided with a dome which external diam. is 50 mm in order to supply a suitable protection of the sensor to the atmospheric agents. The response in accordance with the cosine low has been obtained thanks to the particular shape of the PTFE diffuser and of the housing. The shifting between a theoretical response and the measured one is shown in the figure % shifting from the theorical response Angle Fig.2 The excellent relation between the response of the LP UVA 02 and the cosine low allows to use the instrument also when the sun has a very low raising (the UVA diffuse radiation increases as the sun is leaving the zenith, therefore the error about the direct radiation, owing to the imperfect response according to the cosine low, becomes negligible referred to the measurement of the global radiation). 3 Installation and Mounting of the Radiometer for the Measurement of the Global Radiation: Before installing the radiometer refill the cartridge containing the silica-gel crystals. Silica gel absorbs humidity in the dome chamber; in case of particular climatic conditions this humidity can cause steam on the internal side of the dome and then modify the measurement. Do not touch the silica gel crystals with your hands and do not wet it while refilling the cartridge. Carry out the following instructions in an environment as drier as possible: 1- Loosen the three screws that fix the white shade disk 2- Unscrew the silica gel cartridge using a coin 3- Remove the cartridge perforated cap 4- Open the sachet containing the silica gel (supplied with the radiometer) 5- Replace the silica-gel crystals 6- Close the cartridge with its own cap, paying attention that the sealing O-ring be properly positioned - 2 -

3 7- Screw the cartridge to the radiometer body using a coin 8- Check that the cartridge is screwed tightly (if not, the silica-gel life will be reduced) 9- Position the shade disk and tighten it with the screws 10- The radiometer is ready for use Figure no.3 shows the operations necessary to fill the cartridge with the silica-gel crystals. Fig. 3 Silica-gel cartridge LP SG Sealed sachet of silica gel crystals Perforated cap A B LP G Filling C D The LP UVA 02 has to be mounted in a readily accessible location to be able to provide for a periodic cleaning of the external dome and for the maintenance. Check that no building, construction, tree or obstruction exceeds horizontal plane where the radiometer lays. If this is not possible, select a site where obstructions do not exceed 5 degrees of elevation, in the path followed by the sun, between earliest sunrise and latest sunset. The radiometer has to be located far from any kind of obstruction, which might throw the solar radiation (or its shade) on the radiometer. The LP UVA 02 radiometer is provided with a spirit level for carrying an accurate horizontal leveling. The adjustment is made by means of two leveling screws that allow to adjust the radiometer inclination. Use the two 6mm-diameter holes and a 65mm and a 65mm interaxial distance to mount the instrument on a plane. Remove the shade disk to access the holes and reposition it after mounting (see fig. 4). The LP S1 mounting kit (fig. 5), supplied on demand as an accessory, allows an easy mounting of the radiometer on a mast. The mast maximum diameter shall not exceed 50 mm. The operator shall take care that the mast height does not exceed radiometer plane to avoid measurement errors caused by any reflection or shadow of the mast - 3 -

4 itself. To fix the radiometer to the mounting bracket, remove the shade disk loosening the three screws, fix the radiometer and mount the white shade disk again. It s suggested to thermally isolate the radiometer from its mounting brackets and to check that the electrical contact with the ground be done properly

5 Fixing hole φ 6 mm 52,0 mm 65,0 mm 79,0 mm 160,0 mm Spirit level Leveling screw Fig 4-5 -

6 Max diameter 50 mm LP SP1 LP S1 LP UVA 02 radiometer with bracket LP S1 Fig. 5 4 Electrical Connections and Requirements for Electronic Readout Devices: The LP UVA 02 radiometer does not require any power supply. Two LP UVA 02 are available: with a 5 m output cable (LP UVA 02-5) With a 10 m (LP UVA 02-10). The radiometer is supplied with a PTFE, UV resistant, screened (braid) and 2 wire cable; the colour code is the following: braid braided wire red (+) positive pole of the signal generated by the detector blue (-) negative pole of the signal generated by the detector (in contact with the container) The screen is connected to the container. Figure 6 shows the wiring diagram: - 6 -

7 Photodiode Shield (Black) Blue Red fig. 6 The LP UVA 02 has to be connected either to a millivoltmeter or to a data acquisition system with input impedance bigger than 5MΩ. Typically, the radiometer output signal does not exceed 5-10 mv. In order to better exploit the radiometer features, the readout instrument should have 1µV resolution. 5 Maintenance: It is important to keep the outer domes clean to grant measurement best accuracy. Consequently, the more the dome will be kept clean, the more measurements will be accurate. Washing can be made using water and standard papers for lens, or, in some cases, using pure ETHYL alcohol. After using alcohol, clean again the dome with water only. Because of the high rise/fall in temperature between day and night, some condensation might appear on the radiometer dome. In this case the performed reading is highly overestimated. To minimize the condensation growth, the radiometer is provided with a cartridge containing dessicant material: Silica gel. The efficiency of the Silica gel crystals decreases at the time passing while absorbing humidity. Silica-gel crystals are active when their colour is yellow, while the turn blue as soon as they loose their power. Read instructions at paragraph 3 about how to replace them. Silica gel typical lifetime goes from 2 to 6 months depending on the environment where the radiometer works

8 6 Calibration and Measurements: The radiometer S sensitivity (or calibration factor) allows to determine the irradiance by measuring a signal in Volts at the thermopile ends, which short circuits the photodiode. The S factor is measured in µv/(wm -2 ). Once the difference of potential (DDP) has been measured at the ends of the resistance, the E e irradiance is obtained applying the following formula: E e = DDP/S Where: E e : is the Irradiance expressed in W/m 2, DDP: is the difference of potential measured by the multimeter and expressed in µv, S: is the calibration factor in µv/(w/m 2 ), shown on the radiometer label (and mentioned on the calibration report). Radiometers are factory calibrated one by one and they are marked by their own calibration factor. Calibration is carried our in accordance with the DHLF-E-59 procedure for UVA radiometers calibration procedure. At present this procedure is used at the SIT Calibrating Centre N 124 to calibrate the UVA radiometers; our Centre was accredited to issue SIT certificates according to this procedure (SIT is the Italian Calibration Service for the Italian accreditation which comply with the EA mutual recognition Multilateral Agreement). Calibration is carried out by using the spectral line at 365 nm of a Xe-Mg lamp, suitably filtered, the measurement is carried out by comparison with the primary standard, outfit of the DeltaOhm Metrological Laboratory. In order to fully exploit the LP UVA 02 features it s better to yearly verify the calibration. N.B. At present an international standard for calibrating such a kind of radiometers does not exist; then, in order that the calibration coefficient value makes sense, it s necessary also to specify the procedure followed to get this value. Therefore the user has to consider that the same radiometer calibrated with different procedures can have different sensitivity factors, as explained in the article Source of Error in UV Radiation Measurements, T. C. Larason, C. L. Cromer issued in the Journal of Research of the National Institute of Standards and Technology Vol. 106, Num. 4, (The article is available free of charge in the WEB of the NIST at the following address:

9 7 Technical Features: Typical Sensitivity: µV/(W/m 2 ) Response Time: <0.5 sec (95%) Impedance: KΩ Measuring range: W/m 2 Viewing range: 2π sr Spectral range: 327 nm 384 nm (1/2) 312 nm 393 nm (1/10) 305 nm 400 nm (1/100) Working temperature: -40 C 80 C Response according to the cosine law : < 8 % (between 0 and 80 ) Long-term non stability: < ±3 % (1 year) Non linearity: <1 % Response according to: the temperature < 0.1%/ C Dimensions: figure 4 Weight: 0.90 Kg - 9 -

10 8 Ordering Codes LP UVA 02-5 LP UVA LP S1 LP SP1 Radiometer complete with: shade disk, dessicant sachet with silica gel crystals, 2 silica gel cartridges, spirit level ad Report of Calibration. 5m-long connecting cable. Radiometer complete with: shade disk, dessicant sachet with silica-gel crystals, 2 silica gel cartridges, spirit level and Report of Calibration. 10m-long connecting cable Kit composed of bracket for attachment of the LP UVA 02 radiometer to a mast, complete with leveling screws and fasteners. UV resistant plastic shade disk (BASF LURAN S777K) LP SG LP G Dessicant sachet with silica gel crystals complete with O-ring and cap Pack of 5 cartridges of silica gel crystals